Tectonostratigraphic investigation shows that the Mesozoic (Triassic–Neocomian) allochthonous terranes of the Anadyr–Koryak accretionary region, from the northwestern continental framing of the Pacific Ocean, form isolated tectonic nappes and slices dispersed all over the region, rather than fragments undeformed paleostructures. Nappes and slices of different stratigraphic horizons, derived from various geodynamic and paleolatitudinal environments, have been tectonically amalgamated into the Anadyr–Koryak region. Furthermore, these tectonostratigraphic units are accompanied by slabs of Paleozoic sequences which were also accumulated in various different paleoenvironments.Correlations of the tectonically separated Mesozoic formations are based on the radiolarians, and geochemical and lithologic methods. The tectonostratigraphic units range from Middle Triassic to Hauterivian, and are tectonically arranged in various spatial patterns. Formations of several different geodynamic environments are recognized: oceanic (abyssal plain and MOR), island arcs and marginal basins. The radiolarian assemblages suggest that the Early Mesozoic formations were deposited at different paleolatitudes: Tethyan (Anisian–Sinemurian), North-Tethyan and Boreal (Pliensbachian–Early Bajocian), and in a vast zone from the Equator to South Boreal (Late Bajocian–Hauterivian).Early to Late Mesozoic tectonic paleoenvironments spanned a width greater than 3000 km. This zone was later shortened to a width of 300 km. The development of nappes and slices of the Anadyr–Koryak region, and the Koryak–West Kamchatka orogenic belt on the whole, was due to several collisions near the Asian continental margin. The main collision event occurred in the interval 125–105 Ma.